This project involves studies defining how viruses and their hosts interact in regulating various aspects of virus growth. The biological tools used are bacteriophage lambda and its E. coli host, a well characterized system. We will focus our studies on two areas: 1) The nature of host factors directly involved in the action of virus functions. 2) The nature of silent cryptic prophage genes carried in the E. coli chromosome. Our major approach toward characterizing host factors involved with virus functions is to isolate bacterial mutants in which the virus functions are not active. Using this method we have isolated a series of E. coli mutants in which the lambda N function (which antagonizes transcription termination) is inactive. Characterization of these mutants has permitted us to identify both RNA polymerase and ribosomal proteins directly involved in N action. We plan to extend this study to determine if close linkage between ribosomes and RNA polymerase is involved in the transcription termination-antitermination reactions. We have isolated a variant of phage lambda that efficiently exchanges genetic material with cryptic prophage. We plan to use this phage and other means to characterize the cryptic prophage and determine why these cryptic genes remain unexpressed even though some of them appear to carry all of the regulatory information necessary for their expression.